Chemical compounds having antimicrobial properties have been developed over the years to reduce, eliminate and prevent microbiological growth and proliferation in aqueous systems. These compounds, generally known as cleaners, disinfectants, sanitizers, antiseptics, oxidizers, deodorizers, etc., are placed within an aqueous system to eliminate existing or prevent future microbial growth and are preferred in operation for their automatic nature over alternative methods of controlling microbiological growth which often require frequent user intervention. However, conventional antimicrobial products which are automatically delivered into an aqueous system require periodic user intervention needed to maintain effective concentration levels of antimicrobial species therein.
Conventional antimicrobial products contain at least one active ingredient and may include inert ingredients in combination. Active ingredients or “active agents” are chemical compounds typically containing a halogenated functional group such as chlorine or bromine that achieve concentration levels in aqueous systems capable of destroying microbes by forming compounds such as hypobromous or hypochlorous acid when antimicrobial active agents are dispensed in water. Active agents may generally refer to other useful compounds including water clarifying agents, perfumes, dyes, chelating agents, surfactants, etc. Inert ingredients are any other compounds contained in the product formulation other than the active ingredients. Inert ingredients give additional properties to the antimicrobial product and may include wetting agents, neutralizers, buffering agents, adhesives, acidifying agents, suspension agents, etc., that aid the manufacturing process, control dissolution rates, and facilitate the combination of powders containing the active and inert ingredients into solid forms such as tablets.
Industrial or residential aqueous systems prone to microbiological proliferation that may benefit from the use of antimicrobial compounds include but are not limited to toilets, water storage systems, ponds, pools, hot tubs, water recirculation systems, drinking water, wastewater treatment, etc. In operation, solid forms containing active agents are placed in fluid communication with an aqueous system and dissolution of the active agent from a solid form to a soluble form occurs over time accompanied by an increase in active agent concentration within the fluid of the aqueous system. When an active agent containing a halogen functional group is placed in contact with the water of an aqueous system, for example a toilet tank or placed in the path of water being dispensed into the toilet bowl, the concentration of soluble halogen species in the toilet bowl may increase over time to levels effective for antimicrobial control. When the toilet is flushed, the water containing the soluble active agent is supplied to the toilet bowl to achieve a concentration of halogen capable of microbiological control within the toilet bowl.
Examples of active agents capable of microbiological control typically contain halogenated functional groups including but not limited to: N-chloro-phthalamide, N-bromo-phthalamide, N-dichloro-p-toluene sulphonamide, 2,5-N,N′-dichloroazodicarbonamidine hydrochloride, N,N′-dichloro-dimethylhydantoin, dichloro-5,5-methylethyl hydantoin, N-bromo-N′-chlorodimethyl-hydantoin, N,N′-dibromo-dimethylhydantoin, N-bromo-N-chloro-diphenyl-hydantoin, N,N,N,N-tetrachlorodimethylglycoluracil, N-bromo-N,N-dichloro-dimethylglycoluracil, N,N′-dibromo-dimethyl-glycoluracil, N,N,N,N-tetrachloroglycoluracil, N,N-dichlorodichloroyl, N-bromo-N-chlorosodium cyanurate, dibromo triethylene diamine dihydrochloride, bromo-chlorotriethylene diamine dihydrochloride and N,N,N-trichloro-melamine, trichloro-s-triazinetrione, or combinations thereof. Active agents, referred to herein, may be incorporated into solid forms such as powders or tablets, liquids, gels or other forms suitable to be deployed into an aqueous system of use. Active agents are not limited to those having antimicrobial properties and may be expanded to include any chemical compound which produces a desired effect within an aqueous system. Active agents having antimicrobial properties are referenced as examples herein but such examples are not intended for the purpose of limiting the scope of the invention.
In conventional operation utilizing antimicrobial active agents, a solid tablet or multiple tablets containing at least one antimicrobial active agent or combinations of antimicrobial agents are placed in fluid communication with an aqueous system. Fluid communication may be achieve by placing the active agent directly into the fluid of an aqueous system of use or by creating a fluid circulation path containing the active agent in which fluid is input and subsequently dispensed or released into the aqueous system after contacting and dissolving the active agent. Dissolution of the active agent and release into the fluid of an aqueous system results in a measurable increase in the concentration level of active agent within the fluid. As dissolution continues over time, the tablet volume and surface area simultaneously decrease leading to a gradual decrease in the overall rate of active agent delivery. The decreasing rate of active agent delivery may negatively impact the effectiveness of microbiological control including increasing the amount of time required to reach active agent concentration levels capable of effective antimicrobial control and may also lead to variable active agent concentrations within an aqueous system over the tablet lifetime.
The term “lifetime” with respect to the active agent as referenced herein, will refer to the time period starting when the active agent is introduced into fluid contact with an aqueous system and ending when the active agent has been completely dissolved into the aqueous system. The term “effective lifetime” as referenced herein, will refer to the time period starting when the active agent is introduced into fluid contact with an aqueous system and ending when the active agent dissolves to a point of no longer being capable of achieving a desired function. For example, when referring to the effective lifetime of an antimicrobial active agent in tablet form, dissolution of the tablet until a substantially smaller portion of the tablet remains in the aqueous system, a reduced tablet surface area may limit the ability to achieve a concentration of active agent effective for microbiological control.
The concentration range of active agent effective for microbiological control may be placed within an optimal concentration window bounded by an effective upper concentration limit and an effective lower concentration limit depending on the antimicrobial and solubility properties of the specific active agent or combination of active agents selected. Measured concentration levels of active agent within an aqueous system falling below the lower concentration limit may result in microbiological proliferation and the inability to destroy microbes due to ineffective active agent concentrations whereas concentration levels above the upper concentration limit are wasteful of the active agent and uneconomical to the user. Ideally, constant and controllable concentration levels of active agent are maintained within the aqueous system throughout the tablet lifetime. Maintaining an effective concentration range of active agent may be accomplished by achieving zero-order release of active agent. Zero-order release of active agent may further be defined as supplying active agent into the aqueous system at a rate that does not change substantially with time. The terms “dispense” or “delivery” or “release” may further be defined as either the active or passive transfer or movement of a substance from one position to another position such as the transfer or movement of an active agent from an apparatus housing the active agent and into an aqueous system and are used interchangeably herein without limiting the scope of the invention.
Zero-order release of active agent maintains a consistent and controllable dissolution profile over time allowing a constant amount of active agent to be released into an aqueous system per unit time. However, due to the change in surface area over time, conventional antimicrobial active agents and devices placed within an aqueous system may not be capable of achieving a zero-order release profile. When the dissolution profile of conventional antimicrobial active agents including tablet forms are traced over tablet lifetime, concentrations of active agent higher than the upper concentration limit are achieved in the beginning of the tablet lifetime and concentrations below the lower concentration limit are achieved approaching the end of the tablet lifetime corresponding to a decrease in antimicrobial active agent size and surface area available for dissolution over time. Thus, the amount of active agent supplied at the beginning of the antimicrobial active agent lifetime is excessive and wasteful as concentrations reach higher levels than necessary and the amount of active agent delivered at the end of the antimicrobial active agent lifetime is ineffective for microbiological control due to being below the effective lower concentration limit. As described, the effective lifetime of the tablet is reached prior to complete tablet dissolution resulting in further waste of active agent when the tablet surface area is reduced below levels capable of effective microbiological control. It is desirable to maintain the concentration of active agent within an optimal range throughout the lifetime of the tablet to maximize the antimicrobial efficiency while minimizing or eliminating waste or excessive use of the active agent beyond what is necessary for effective microbiological control. It is further desirable to increase both the active agent lifetime and effective lifetime beyond the lifetimes of conventional active agents.
The lifetimes of conventional antimicrobial active agents and devices typically range from 1-4 months, for example when antimicrobial active agent tablets are used for microbiological control in a toilet. Users may find it preferable to maximize the lifetime of the tablet so as to reduce the frequency of tablet replacement and associated replacement costs so as to maximize the cost effectiveness of antimicrobial products. Increasing tablet lifetime has been proposed in the prior art and methods include increasing the tablet size, modifying the tablet composition including the addition of a longevity agent having a slower dissolution rate than the active agent so as to reduce the overall dissolution rate, applying higher pressure compression of the tablet during manufacture, and multilayered or multi-component tablets. However, problems maintaining optimal concentrations of active agent arise when the methods described are reduced to practice.
Increasing the size of the tablet as a means of increasing tablet lifetime yields active agent concentrations higher than the upper concentration limit resulting in waste of the active agent as excessive concentrations are achieved in addition to other adverse effects including damage to components of an aqueous system. In addition, high concentrations of chlorine containing active agents may produce an undesirable chlorine odor noticeable to the user. Increasing the size of the tablet increases manufacturing costs which are passed on to the consumer at an economic disadvantage given that more active agent will be used than is necessary for effective microbiological control near the beginning of the tablet lifetime. For the combined purpose of increasing the lifetime of the tablet, maintaining zero-order release of active agent, and keeping active agent concentrations within an optimal concentration window bounded by upper and lower concentration limits, it is desirable to place a larger quantity of active agent into an aqueous system such as by increasing the tablet volume or quantity of tablets while at the same time, controlling the amount of active agent released into an aqueous system per unit time.
Decreasing tablet solubility and thereby, the rate of dissolution by using additives in the composition of the tablet or increasing the compression ratio during tablet manufacture are effective at increasing the lifetime of the tablet but may reduce the concentration of active agent to levels below the lower effective concentration limit, thus, negatively impacting the ability to prevent microbiological proliferation. Further, the use of inert additives for the purpose of controlling the overall tablet dissolution rate which do not contribute to the antimicrobial properties of the tablet will reduce the value delivered to the user by reducing the amount of active agent in the tablet and may increase the tablet's manufacturing complexity and cost.
The use of multi-layered tablets having a low solubility region surrounding a region of higher solubility may also increase the lifetime of the tablets but also increase manufacturing costs and complexity. To benefit the user economically, it is desirable to increase the lifetime of the tablet while maintaining optimal concentration levels of active agent within an aqueous system without impacting tablet manufacturability or production costs.
Handling of chemical products may pose a health risk to the end user due to the strong oxidizing effects of antimicrobial active agents. Conventional antimicrobial tablets containing an active agent are commonly packaged in child resistant films that require the user to cut open the package to gain access to the tablet. Cutting the packaging open and exposing the tablet places the user at risk of chemical contact especially if the user must manually place the product within an aqueous system such as a toilet tank. It is desirable to provide an apparatus which limits or eliminates the user's risk for chemical exposure.
Devices containing an active agent which are disposed directly into an aqueous system often have multiple parts which add complexity during manufacturing. It is desirable to produce a device capable of microbiological control in aqueous systems that may be manufactured at a low cost and in a simple manner. Devices designed to be placed directly into the toilet bowl are visible to the user and may be undesirable. To improve aesthetic value, it is desirable for the microbiological control device to be hidden from view of the user such as by placement into the tank of the toilet.
Aqueous systems in which an active agent is disposed may have frequent exchanges of water that replace water containing a measurable concentration of active agent with fresh water or water having a lower concentration of active agent. For example, a system such as a toilet in which the water in contact with the active agent is exchanged frequently with fresh water may require a higher surface area of exposure of active agent to achieve a given concentration of active agent within a given period of time between water exchanges compared to a system in which the water is exchanged less frequently. For the purpose of achieving a desired concentration of active agent within an aqueous system, it is desirable to enable metered or incremental amounts of active agent into an aqueous system depending on the frequency that water is exchanged within the system. In operation, a user may place multiple units of the microbiological control apparatus into a toilet that is frequently flushed while reducing the number of units placed within a toilet that is less frequently flushed. The ability to control the number of units supplied to an aqueous system also prevents using excessive amounts of active agent especially in aqueous systems having a fluid that is less frequently exchanged. Active agents and devices known in the prior art may not provide the ability to modify the amount of active agent delivered into an aqueous system.